The present invention relates generally to the aerodynamic performance of a gas turbine engine variable vane. More particularly, in one embodiment of the present invention a winglet is attached to one end of a variable vane so as to reduce end wall losses resulting from air leakage from the high pressure to the low-pressure side of the airfoil. Although, the present invention was developed for use in a gas turbine engine, certain applications may be outside of this field.
It is well known in the gas turbine engine field that the performance of the engine over its cycle may be improved by utilizing variable position airfoils within various portions of the engine. By way of example, some engines utilize variable vanes in the compressor section of the engine in order to provide improved performance at off-design operating conditions. The variable vanes rotate between a relatively closed position under low power conditions and a fully open position under full power conditions. The clearance between the vanes and the walls of the flow passageway allows leakage from the high-pressure side to the low-pressure sides of the vane which has an adverse effect upon engine performance. Larger clearances cause greater losses in performance.
Vanes are often classified according to their aspect ratio which defines a relationship between the vane's radial span and its chordal span. A conventional high aspect ratio variable vane comprises an airfoil, a boss/button, a spindle, and a rotational axis. The boss/button provides a structural transition from the airfoil to the spindle, and covers the inner diameter end and outer diameter end of the airfoil. The coverage of the ends is desirable since it minimizes endwall losses due to leakage flow at the endwall gap between the vanes and the walls of the flow passageway.
As compression system technology level increases, the airfoil aspect ratio typically decreases. A variable vane having a reduced aspect ratio results in reduced coverage by the boss/button at the airfoil inner diameter end and airfoil outer diameter end. The reduction in coverage is a result of geometric limits on button diameter causing a higher percentage of the airfoil chord to have an endwall gap. Further, the reduced coverage by the button/boss of the airfoil often causes a decreased dynamic performance due to a decrease in airfoil stiffness. Therefore, as the airfoil aspect ratio decreases there is often a performance penalty, both aerodynamic and structurally.
Heretofore, there has been a need for a winglet for improving the aerodynamic performance of a gas turbine engine variable vane by reducing endwall losses resulting from fluid losses from the high pressure to the low-pressure side of the airfoil. The present invention satisfies this need in a novel and unobvious way.